Attrition resistant gamma-alumina catalyst support

ABSTRACT

A γ-alumina catalyst support having improved attrition resistance produced by a method comprising the steps of treating a particulate γ-alumina material with an acidic aqueous solution comprising water and nitric acid and then, prior to adding any catalytic material thereto, calcining the treated γ-alumina.

This application is a continuation of application Ser. No. 09/844,379filed Apr. 27, 2001, now U.S. Pat. No. 6,740,621 which is a divisionalof U.S. patent application Ser. No. 09/316,562, filed May 21, 1999, nowU.S. Pat. No. 6,262,132.

The Government of the United States of America has rights to thisinvention pursuant to Contract No. DE-AC22-92 PC92108 awarded by theU.S. Department of Energy.

BACKGROUND OF THE INVENTION

1. Technical Field

In one aspect, this invention relates to methods of reducing catalystattrition losses for hydrocarbon synthesis processes conducted in highagitation reaction systems. More particularly, but not by way oflimitation, the present invention relates to methods of reducingcatalyst attrition losses for hydrocarbon synthesis processes conductedin three-phase reaction systems. In another aspect, this inventionrelates generally to attrition resistant catalysts for conductingFischer-Tropsch synthesis.

2. Background

In Fischer-Tropsch processes, synthesis gases comprising carbon oxidesand hydrogen are reacted in the presence of Fischer-Tropsch catalysts toproduce liquid hydrocarbons. Fischer-Tropsch synthesis processes aremost commonly conducted in fixed bed, gas-solid or gas-entrainedfluidized bed reaction systems, fixed bed reaction systems being themost commonly used. It is recognized in the art, however, that slurrybubble column reactor systems offer tremendous potential benefits overthese commonly used Fischer-Tropsch reaction systems. However, thecommercial viability of slurry bubble column processes has beenquestioned. The unique reaction conditions experienced in slurry bubblecolumn processes are extremely harsh. Thus, catalyst attrition losses inslurry bubble column processes can be both very high and costly. Infact, many of the best performing catalysts employed in otherFischer-Tropsch reaction systems quickly break down when used in slurrybubble column systems.

Heretofore, little has been done to even evaluate or model the harshconditions experienced in slurry bubble column reactor processors, muchless solve the attrition loss problem. Thus, a need presently exists fora means of both (a) reducing catalyst attrition losses and (b)increasing the viability of higher performance catalysts in slurrybubble column processes and in other such “high agitation” reactionsystems.

As mentioned above, the synthesis gas, or “syngas,” used inFischer-Tropsch processes is typically a mixture consisting primarily ofhydrogen and carbon oxides. Syngas is typically produced, for example,during coal gasification. Processes are also well known for obtainingsyngas from other hydrocarbons, including natural gas. U.S. Pat. No.4,423,265 to Chu et al. notes that the major processes for producingsyngas depend either upon the partial combustion of a hydrocarbon fuelwith an oxygen-containing gas or the reaction of the fuel with steam, oron a combination of these two reactions. U.S. Pat. No. 5,324,335 toBenham et al., explains the two primary methods (i.e., steam reformingand partial oxidation) for producing syngas from methane. TheEncyclopedia of Chemical Technology, Second Edition, Volume 10, pages3553–433 (1966), Interscience Publishers, New York, N.Y. and ThirdEdition, Volume 11, pages 410–446 (1980), John Wiley and Sons, New York,N.Y. is said by Chu et al. to contain an excellent summary of gasmanufacture, including the manufacture of synthesis gas.

It has long been recognized that syngas can be converted to liquidhydrocarbons by the catalytic hydrogenation of carbon monoxide. Thegeneral chemistry of the Fischer-Tropsch synthesis process is asfollows:CO+2H₂→(—CH₂—)+H₂O  (1)2CO+H₂→(—CH₂—)+CO₂  (2)The types and amounts of reaction products, i.e., the lengths of carbonchains, obtained via Fischer-Tropsch synthesis vary dependent uponprocess kinetics and the catalyst selected.

Many attempts at providing active catalysts for selectively convertingsyngas to liquid hydrocarbons have previously been disclosed. U.S. Pat.No. 5,248,701 to Soled et al., presents an over-view of relevant priorart. The two most popular types of catalysts heretofore used inFischer-Tropsch synthesis have been iron-based catalysts andcobalt-based catalysts. U.S. Pat. No. 5,324,335 to Benham et al.discusses the fact that iron-based catalysts, due to their high watergas shift activity, favor the overall reaction shown in (2) above, whilecobalt-based catalysts tend to favor reaction scheme (1).

Recent advances have provided a number of catalysts active inFischer-Tropsch synthesis. Besides iron and cobalt, other Group VIIImetals, particularly ruthenium, are known Fischer-Tropsch catalysts. Thecurrent practice is to support such catalysts on porous, inorganicrefractory oxides. Particularly preferred supports include silica,alumina, silica-alumina, and titania. In addition, other refractoryoxides selected from Groups III, IV, V, VI and VIII may be used ascatalyst supports.

The prevailing practice is to also add promoters to the supportedcatalyst. Promoters can include ruthenium (when not used as the primarycatalyst component), rhenium, hafnium, cerium, and zirconium. Promotersare known to increase the activity of the catalyst, sometimes renderingthe catalyst three to four times as active as its unpromotedcounterpart.

Contemporary cobalt catalysts are typically prepared by impregnating thesupport with the catalytic material. As described in U.S. Pat. No.5,252,613 to Chang et al., a typical catalyst preparation may involveimpregnation, by incipient wetness or other known techniques, of, forexample, a cobalt nitrate salt onto a titania, silica or aluminasupport, optionally followed or preceded by impregnation with a promotermaterial. Excess liquid is then removed and the catalyst precursor isdried. Following drying, or as a continuation thereof, the catalyst iscalcined to convert the salt or compound to its corresponding oxide(s).The oxide is then reduced by treatment with hydrogen, or ahydrogen-containing gas, for a period of time sufficient tosubstantially reduce the oxide to the elemental or catalytic form of themetal. U.S. Pat. No. 5,498,638 to Long points to U.S. Pat. Nos.4,673,993, 4,717,702, 4,477,595, 4,663,305, 4,822,824, 5,036,032,5,140,050, and 5,292,705 as disclosing well known catalyst preparationtechniques.

As also mentioned above, Fischer-Tropsch synthesis has heretofore beenconducted primarily in fixed bed reactors, gas-solid reactors, andgas-entrained fluidized bed reactors, fixed bed reactors being the mostutilized. U.S. Pat. No. 4,670,472 to Dyer et al. provides a bibliographyof several references describing these systems. The entire disclosure ofU.S. Pat. No. 4,670,472 is incorporated herein by reference.

In contrast to these other hydrocarbon synthesis systems, slurry bubblecolumn reactors are “three phase” (i.e., solid, liquid, and gas/vapor)reaction systems involving the introduction of a fluidizing gas into areactor containing catalyst particles slurried in a hydrocarbon liquid.The catalyst particles are slurried in the liquid hydrocarbons within areactor chamber, typically a tall column. Syngas is then introduced atthe bottom of the column through a distributor plate, which producessmall gas bubbles. The gas bubbles migrate up and through the column,causing beneficial agitation and turbulence, while reacting in thepresence of the catalyst to produce liquid and gaseous hydrocarbonproducts. Gaseous products are captured at the top of the SBCR, whileliquid products are recovered through a filter which separates theliquid hydrocarbons from the catalyst fines. U.S. Pat. Nos. 4,684,756,4,788,222, 5,157,054, 5,348,982, and 5,527,473 reference this type ofsystem and provide citations to pertinent patent and literature art. Theentire disclosure of each of these patents is incorporated herein byreference.

It is recognized that conducting Fischer-Tropsch synthesis using a SBCRsystem could provide significant advantages. As noted by Rice et al. inU.S. Pat. No. 4,788,222, the potential benefits of a slurry process overa fixed bed process include better control of the exothermic heatproduced by the Fischer-Tropsch reactions, as well as better maintenanceof catalyst activity by allowing continuous recycling, recovery andrejuvenation procedures to be implemented. U.S. Pat. Nos. 5,157,054,5,348,982, and 5,527,473 also discuss advantages of the SBCR process.

Although the use of slurry bubble column reactors for commercialapplications offers significant potential advantages over fixed bed andother types of reactor systems, the viability of the slurry bubblecolumn process has heretofore been questioned, owing in large part tohigh catalyst attrition losses and costs. As mentioned above, slurrybubble column reactor processes are extremely demanding on catalystsfrom a physical strength standpoint. Many catalyst formulations lack anypractical application in SBCR's because of the rate of physicalattrition experienced. In addition to catalyst loss, the physicaldestruction and attrition of the catalyst results in (a) poorerdistribution of the catalyst in the reactor, (b) filtration problems inremoving liquid products, and (c) possible contamination of the productswith catalytic material.

The significance of the attrition problem was seen, for example, duringthe Fischer-Tropsch Demonstration Run III conducted in October 1996 atthe U.S. Department of Energy's Alternative Fuels Development Unit (aslurry bubble column reactor) in LaPorte, Tex. (See Brown et al., inPaper 27E for AICHEME Meeting in Houston, Mar. 10, 1997). The catalystselected for that demonstration was a promising, “improved” cobaltcatalyst which exhibited high activity in laboratory tests. However, theLaPorte run had to be terminated when the catalyst unexpectedly brokedown and seriously plugged the process filters.

As this example also suggests, most of the work performed heretofore inFischer-Tropsch catalyst development has focused on the activity and/orselectivity of the catalysts, with little or no attention being given totheir physical or mechanical properties. Most catalysts have beendesigned for fixed bed reaction systems, which are much less demandingin terms of attrition resistance than are slurry bubble column reactors.

Recently, U.S. Pat. Nos. 5,648,312, 5,677,257, and 5,710,093 disclosedformulations of hydrogenation catalysts which are said to provideimproved attrition resistance. The catalyst supports used in theseformulations are substantially spherical particles consisting ofsubstantially homogeneous mixtures of silica particles and siliconcarbide particles.

It is known that the use of spheroidal supports in the preparation ofsupported metal catalysts for fluidized bed applications tends to reducecatalyst attrition. However, the mere use of spherical supports is notsufficient, in and of itself, to obtain acceptable attrition resistancefor slurry bubble column applications.

SUMMARY OF THE INVENTION

The present invention satisfies the needs and resolves the problemsdiscussed above. The invention provides a method for reducing catalystattrition losses in hydrocarbon synthesis processes conducted in highagitation reaction systems, particularly in three-phase reactionsystems. As used herein and in the claims, the phrase “high agitationreaction systems” refers to slurry bubble column reactor systems and toother reaction systems wherein catalyst attrition losses, resulting fromfragmentation, abrasion, and other similar or related mechanisms, atleast approach the attrition losses experienced in slurry bubble columnsystems.

In one aspect, the inventive method comprises the step of reacting asynthesis gas in a high agitation reaction system in the presence of acatalyst comprising a γ-alumina support, wherein the γ-alumina supportincludes an amount of titanium or titania effective for increasing theattrition resistance of the catalyst. The titanium or titania willpreferably be present in the γ-alumina support in an amount of not lessthan 800 parts per million (ppm) by weight of titanium.

In another aspect, the inventive method for reducing catalyst attritionlosses in hydrocarbon synthesis processes conducted in high agitationreaction systems comprises the step of reacting a synthesis gas in ahigh agitation reaction system in the presence of a catalyst comprisinga γ-alumina support which has been treated, after calcination, with anacidic, aqueous solution. The acidic, aqueous solution will preferablyhave a pH of not more than 5.

In yet another aspect, the inventive method for reducing catalystattrition losses in hydrocarbon synthesis processes conducted in highagitation reaction systems comprises the step of reacting a synthesisgas in a high agitation reaction system in the presence of a catalystcomprising cobalt on a γ-alumina support wherein the cobalt is presentin an amount in the range of from about 10 parts by weight (pbw) toabout 70 pbw, per 100 pbw of the γ-alumina support, and the cobalt hasbeen applied to the γ-alumina support by totally aqueous impregnationusing an effective aqueous solution composition, and an effective amountof the aqueous solution, to achieve incipient wetness of the γ-aluminasupport with the desired amount of cobalt. The aqueous solutionpreferably has a pH of not more than about 5.

In yet another aspect, the inventive method for reducing catalystattrition losses in hydrocarbon synthesis processes conducted in highagitation reaction systems comprises the step of reacting a synthesisgas in a high agitation reaction system in the presence of a catalystwherein the catalyst comprises cobalt on a γ-alumina support and thecatalyst further comprises an amount of lanthana promoter effective forincreasing the attrition resistance of the catalyst. The amount ofcobalt present in the catalyst is preferably in the range of from about10 pbw to about 70 pbw, per 100 pbw of the γ-alumina support. The amountof lanthana present in the catalyst is preferably in the range of fromabout 0.5 to about 8 pbw, per 100 pbw of the γ-alumina support.

In yet another aspect, the inventive method for reducing catalystattrition losses in hydrocarbon synthesis processes conducted in highagitation reaction systems comprises the step of reacting a synthesisgas in a high agitation reaction system in the presence of a catalystcomprising a γ-alumina support, wherein said γ-alumina support isproduced from boehmite having a crystallite size, in the 021 plane, inthe range of from about 30 to about 55 Ångstroms.

In one preferred embodiment of the inventive method, the high agitationreaction system is a three phase (i.e., solid, liquid, and gas/vapor)reaction system. In a particularly preferred embodiment of the inventivemethod, the high agitation reaction system is a slurry bubble columnreaction system.

The present invention also provides a method of producing anattrition-resistant catalyst. The catalyst produced by the inventivemethod includes a calcined γ-alumina support. In one aspect, thisinventive method comprises the step, after calcination of the supportbut before adding catalytic materials thereto, of treating the supportwith an acidic, aqueous solution having an acidity level effective forincreasing the attrition resistance of the catalyst. The presentinvention also provides an attrition resistant catalyst produced by theinventive method.

The present invention further provides a method of producing anattrition-resistant catalyst support. The inventive method for producingan attrition-resistant catalyst support comprises the step of treatingcalcined γ-alumina with an acidic, aqueous solution having an aciditylevel effective for increasing the attrition resistance of the calcinedalumina. The present invention also provides an attrition-resistantcatalyst support produced by the inventive method.

Further objects, features, and advantages of the present invention willbe apparent upon examining the accompanying drawings and upon readingthe following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a graph comparing the Fischer-Tropsch synthesisperformances in fixed bed and slurry bubble column reactors of promotedcobalt catalysts supported on alumina, silica, and titania.

FIG. 2 provides a graph showing the effect of titanium concentration onthe activities of ruthenium-promoted, cobalt-on-alumina catalysts.

FIG. 3 provides a schematic diagram of a Jet Cup system used forconducting attrition resistance tests.

FIG. 4 provides a schematic diagram of an ultrasonic system used forconducting attrition resistance tests.

FIG. 5 provides a graph comparing the particle size distributions ofsilica-supported cobalt catalysts before and after SBCR, Jet Cup andultrasound attrition tests.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Catalyst Compositions

The present invention provides supported cobalt catalysts which are wellsuited for use in Fischer-Tropsch synthesis processes. These catalystsare particularly well suited for use in three-phase reactor processesand other high agitation reaction systems. Examples of general catalystcompositions provided by the present invention include: (a) cobalt,without any promoter, preferably supported on γ-alumina or dopedγ-alumina; (b) cobalt, with one or more noble metal promoters,preferably supported on γ-alumina or doped γ-alumina; (c) cobalt,promoted with both a noble metal promoter and one or more selectivitypromoters (preferably an alkali or rare earth oxide), preferablysupported on γ-alumina or doped γ-alumina; and (d) cobalt, promoted withone or more selectivity promoters and without a noble metal promoter,preferably supported on γ-alumina or doped γ-alumina. Examples oftypical promoters include, but are not limited to, noble metals such asruthenium, metal oxides such as oxides of zirconium, lanthana, orpotassium, and other oxides of elements from Groups IA, IIA, IVA, VA,and VIA.

Preferred catalyst compositions comprise (per 100 parts by weight ofsupport): from about 10 to about 70 pbw cobalt; from about 0.1 to about8 pbw ruthenium (when present); from about 0.1 to about 8 pbw potassium(when present); and from about 0.5 to about 8 pbw lanthana (whenpresent). The catalyst can also include other promoter materials. Wehave discovered that, to obtain a particularly desirable combination ofattrition resistance, selectivity, and activity, particularly in highagitation reaction systems such as slurry bubble column reactors, thecatalysts will most preferably comprise (per 100 parts by weight ofsupport): from about 15 to about 55 pbw (more preferably from about 20to about 45 pbw) cobalt; from about 0.2 to about 1.5 pbw ruthenium (whenpresent); from about 0.2 to about 1.0 pbw potassium (when present); andfrom about 0.5 to about 5.0 pbw (most preferably from about 0.9 to about2.5 pbw) lanthana (when present).

The Catalyst Support

FIG. 1 shows that, for cobalt catalysts used in both fixed bed and aslurry bubble column reactor systems, the particular support employedplays a major role in influencing the overall hydrocarbon productionrate (i.e., catalyst activity) with little or no effect on productselectivity. For the supports tested, catalyst activities ranked in thefollowing order: Al₂O₃>SO₂>>TiO₂. With respect to alumina supports,comparisons with literature data and additional tests revealed that thesource of the alumina and the pretreatment procedures used also playmajor roles in determining the performance of the resulting,cobalt-based, Fischer-Tropsch catalysts.

All titania-supported cobalt catalysts tested, with or withoutpromoters, were found to have poor Fischer-Tropsch synthesis propertiesin both fixed bed and SBCR systems. Compared to γ-alumina and silica,titania supports have much lower surface areas and pore volumes. Thus,they do not readily retain high cobalt loadings.

Although having relatively high surface areas, silica-supported cobaltcatalysts showed low Fischer-Tropsch synthesis performance.Silica-supported cobalt catalysts are unstable in reaction conditions,such as those usually encountered in Fischer-Tropsch reaction systems,where a significant amount of water is present. The formation ofcobalt-silica compounds under these conditions is believed to cause thislower performance. To prevent or at least slow down silicate formation,the silica surface must typically be coated with oxide promoters, suchas ZrO₂, prior to cobalt impregnation.

Characteristics and Preparation of Preferred Alumina Supports

The catalyst support employed in the present invention is preferably aγ-alumina support having: a low level of impurities, especially sulfur(preferably less than 100 ppm sulfur); a spheroidal shape; an averageparticle size in the range of from about 10 to about 150 μm (mostpreferably from about 20 to about 80 microns); a BET surface area, aftercalcination, in the range of from about 200 to about 260 m²/g; and aporosity in the range of from about 0.4 to about 1.0 cm³/g.

The alumina support is preferably produced from relatively high purity,synthetic boehmite. As discussed hereinbelow, the boehmite can be formedfrom aluminum alkoxide of the type obtained in the manufacture ofsynthetic fatty alcohols. Alternatively, suitable, high purity boehmitematerials can be formed from aluminum alkoxide produced byalcohol/aluminum metal reaction processes.

The aluminum alkoxide is preferably hydrolyzed to produce high purity,synthetic, monohydrate alumina. Next, this material is preferablyspray-dried to yield highly porous, spherical boehmite particles ofrelatively high surface area. The particulate boehmite material ispreferably then sieved to remove fines and large particles so that adesired particle size range is obtained (most preferably from about 20to about 80 microns). The sieved material is calcined to convert theboehmite particles to a γ-alumina support material having the desiredsurface area and porosity. The boehmite material will preferably becalcined at a temperature of at least 350° C. (more preferably fromabout 400° C. to about 700° C. and most preferably about 500° C.) for aperiod of from about 3 to about 24 hours (more preferably from about 5to about 16 hours and most preferably about 10 hours). The desiredcalcination temperature is preferably reached by slowly heating thesystem at a rate of about 0.5–2.0° C./minute.

As shown in the examples presented hereinbelow, we have discovered thatthe attrition resistances of the supported catalyst are unexpectedlyimproved when the alumina support is formed from a synthetic boehmitehaving a crystallite size (in the 021 plane) in the range of from about30 to about 55 Ångstroms, preferably in the range of from about 40 toabout 50 Ångstroms. As will be understood by these skilled in the art,the boehmite production process can be readily controlled to obtaindesired crystallite sizes within these ranges.

For a given set of calcining conditions, the crystallite size of theboehmite material determines the average pore size, the pore sizedistribution, and the surface area of the calcined γ-alumina materialobtained. As the boehmite crystallite size increases, the surface areaof the calcined alumina product decreases and the average pore radius ofthe calcined alumina product increases. We have discovered that,generally, decreasing the average pore radius of the calcined aluminamaterial increases its attrition resistance.

Examples of commercially-supplied boehmite materials suitable forforming the preferred γ-alumina supports employed in the presentinvention include the CATAPAL and PURAL aluminas supplied byCondea/Vista. As discussed below, commercial materials of this type areparticularly effective when intentionally produced to have certaintargeted titanium “impurity” levels. Product quality reports for theCATAPAL aluminas indicate that these products, as presently produced andsold, can have titania impurity levels varying all the way up to 3000ppm of elemental titanium by weight. The PURAL products, on the otherhand, typically have varying titanium impurity levels of up to about 600ppm.

Titanium Doping of γ-Alumina Supports

As shown hereinbelow, we have discovered that the presence of titaniumin the γ-alumina support material unexpectedly and surprisingly improvessignificantly the attrition resistance of γ-alumina-supportedFischer-Tropsch catalysts used in high agitation reaction systems. Thetitanium dopant will preferably be present in the γ-alumina support inan amount of at least 800 ppm of titanium by weight. The dopant willmore preferably be present in the support in an amount in the range offrom about 800 ppm to about 2000 ppm of titanium and will mostpreferably be present in an amount in the range of from about 1000 toabout 2000 ppm. The titanium dopant can be added at substantially anytime but will most preferably be added prior to crystallization of theboehmite.

As is well known to those skilled in the art, one method of producingsynthetic boehmite materials utilizes aluminum alkoxides recovered asbyproducts of certain processes (e.g., the Ziegler Process) employed formanufacturing synthetic fatty alcohols. The Ziegler Process typicallycomprises the steps of: (1) reacting high purity alumina powder withethylene and hydrogen to produce aluminum triethyl; (2) polymerizingethylene by contacting it with the aluminum triethyl, thus resulting inthe formation of aluminum alkyls; (3) oxidizing the aluminum alkyls withair to produce aluminum alkoxides; and (4) hydrolizing the aluminumalkoxides to produce alcohols and an alumina byproduct. The oxidationstep of the Ziegler process is typically catalyzed by an organictitanium compound which is itself converted to titanium alkoxide. Thetitanium alkoxide remains with and is co-hydrolized with the aluminumalkoxide, thus resulting in an alumina byproduct which is “doped” with asmall amount of titania.

Another process for forming synthetic boehmite utilizes aluminumalkoxide produced by reacting an alcohol with a highly pure aluminumpowder. The aluminum alkoxide is hydrolyzed to produce an alcohol, whichis recycled for use in the alkoxide formation step, and alumina. Becausethis process does not involve an oxidation step, the alumina producttypically does not contain titanium. However, for purposes of thepresent invention, any desired amount of titanium dopant can be includedin the alumina product by, for example, adding a titanium alkoxide to,and co-hydrolyzing the titanium alkoxide with, the aluminum alkoxide. Ifdesired, the same process can be used to add other dopants such as, forexample, silica, lanthanum, or barium.

Heretofore, support manufacturers and catalyst users have simplyconsidered titania, if present in the alumina support, to be a harmlessimpurity. Of the commercial synthetic boehmite products presentlyavailable in the market, some are produced by the Ziegler process,others are produced by the above-described aluminum alkoxide hydrolysisprocess, and still others are produced by a combination of theseprocesses wherein the resulting products or product precursors areblended together. Such products are sold and used interchangeably,without regard to the small amount, if any, of the titania present.

Thus, the amount of titanium present in commercial γ-alumina supportscan vary from 0 ppm to as high as 3000 ppm titanium by weight or more.Titanium concentrations can also vary significantly between differentbatches of the same commercial product.

As mentioned above, because the fixed bed and other reaction systems nowcommonly used are much less severe, the art has focused primarily onimproving the activity and/or selectivity of Fischer-Tropsch catalysts.FIG. 2 illustrates the detrimental effect of titania on the activitiesof ruthenium promoted, cobalt-on-alumina catalysts. FIG. 2 shows theactivities (g-HC/kg-cat/hr) of three catalysts (catalysts 20, 23, and24) which were produced and tested as described hereinbelow in Example7. Catalysts 20, 23, and 24 were identical in all respects except thatcatalyst 24 was formed on a γ-alumina support found to have a titaniaconcentration, expressed as titanium, of about 7 ppm by weight, catalyst23 was formed on a γ-alumina support found to have a titaniumconcentration of about 500 ppm, and catalyst 20 was formed on aγ-alumina support found to have a titanium concentration of about 1000ppm. FIG. 2 shows that, as the amount of titania in the supportincreased, the activity of the catalyst declined from about 1340 forcatalyst 24, to about 1322 for catalyst 23, and to about 1112 forcatalyst 20. Thus, any preference in the art as to the presence oftitanium would heretofore have been that no titania dopant be includedin the γ-alumina support.

We have discovered, however, that the intentional inclusion ofcontrolled amounts of titanium in γ-alumina supports unexpectedly andsurprisingly reduces catalyst attrition losses in high agitationreaction systems to such a degree as to greatly outweigh any incidentalreduction in catalyst activity. The improvement provided by ourdiscovery is particularly effective for addressing the uniquely harshconditions experienced in slurry bubble column and other three-phasereaction systems. In fact, this discovery could be said to actuallyincrease the catalyst activities obtainable in high agitation reactionsystems by now allowing certain “higher performance” catalysts to beused in these systems.

Catalyst Preparation

The catalytic components of the preferred catalysts are preferably addedto the support by totally aqueous impregnation using appropriate aqueoussolution compositions and volumes to achieve incipient wetness of thesupport material with the desired metal loading(s). Promoted catalystsare most preferably prepared by totally aqueous co-impregnation.Examples of typical promoters include, but are not limited to: noblemetals; metal oxides such as oxides of Zr, La, K; and other oxides ofelements from Groups IA, IIA, IVA, VA, and VIA.

In accordance with the present invention, the totally aqueousimpregnation of cobalt onto the support, with or without one or moredesired promoters, is preferably accomplished by the steps of: (a)calcining the alumina support in the manner described above; (b)impregnating the support with an aqueous solution of cobalt nitrate, orof cobalt nitrate and one or more promoter compounds (preferably one ormore promoter-nitrates [e.g., ruthenium (III) nitrosyl nitrate] and/orpromoter-chlorides [e.g., ruthenium III chloride], most preferablypromoter-nitrates) using a sufficient quantity of the solution toachieve incipient wetness with a desired loading of cobalt and of anydesired promoter(s); (c) drying the resulting catalyst precursor forabout 5–24 hours at approximately 80–130° C., with moderate mixing, toremove solvent water and obtain a dried catalyst; and (d) calcining thedried catalyst in air or nitrogen by slowly raising the temperature ofthe system at a rate of about 0.5–2.0° C. per minute to approximately250–400° C. and then holding for at least 2 hours to obtain the oxideform of the catalyst. Multiple impregnation/coimpregnation steps (b) canbe used when higher cobalt loadings are desired.

The preferred cobalt nitrate concentrations employed for aqueousimpregnation and aqueous co-impregnation typically provide pH values inthe 1–3 range. As shown hereinbelow, pH values within this rangeunexpectedly and surprisingly provide a significant improvement inattrition resistance.

As one example, a particularly preferred ruthenium-promoted cobaltcatalyst is prepared according to the following procedure. First, thesupport, preferably γ-alumina, is calcined at from about 400° C. toabout 700° C., preferably about 500° C., for about 10 hours. Thecalcined support is then impregnated with an aqueous solution containingboth cobalt nitrate [Co(NO₃)₂-6H₂O] and ruthenium (III) nitrosyl nitrate[Ru(NO)(NO₃)₃-xH₂O] using an appropriate quantity to achieve incipientwetness with the desired loadings of cobalt and ruthenium. The resultingcatalyst precursor is then dried for 5 hours at 115° C. with moderatestirring in order to remove the solvent water. The dried catalyst isthen calcined in air by raising its temperature at a rate of 1° C./minto 300° C. and holding for at least 2 hours.

In another example, a doubly promoted cobalt catalyst can be prepared ina similar fashion using a second promoter nitrate (e.g., potassiumnitrate [KNO₃] or lanthanum nitrate [La(NO₃)₃.H₂O]) dissolved in thesame solution which contains the cobalt and ruthenium compounds.

Acceptable ruthenium salts, such as those used in the present invention,have very limited aqueous solubilities. These salts are only moderatelysoluble in cold water and, when heated in an effort to increasesolubility, tend to decompose and precipitate. However, by using theaqueous co-impregnation method of the present invention, superiorruthenium-promoted catalysts having the desired concentration rangescited above can be produced without difficulty.

Until recently, ruthenium-promoted cobalt catalysts were typicallyprepared by coprecipitation of the metal components onto the supportmaterial. Such methods typically do not yield well dispersed systems,and therefore result in an inefficient use of the active metals.Coprecipitation methods generally also involve the use of two solutions,the first containing the support material and the dissolved promotersalt(s) and the second containing a precipitating agent (e.g., potassiumcarbonate). The solutions must be employed in relatively largequantities, typically several orders of magnitude larger than used inincipient wetness impregnation.

Due to the shortcomings of coprecipitation processes, impregnationtechniques have become the preferred means of putting cobalt and itspromoters onto porous supports. However, whenever ruthenium has beenused as a promoter, the impregnation methods have employed an organicruthenium precursor dissolved in an organic solvent. This use of organicsolvents as the impregnating media for ruthenium promoters has, ofcourse, resulted from the poor aqueous solubility characteristics of thepractical ruthenium salts. Incipient wetness impregnation utilizes arelatively minute amount of impregnation solution. The amount ofsolution employed is typically only an amount sufficient to fill thepores of the support material. However, the promoter salt(s) must becompletely dissolved in this small amount of solution.

When an organic impregnation method is used, the drying step involvesthe evaporation of the organic solvent, which requires someenvironmentally acceptable way of disposing of the solvent vapor. Inaddition, special explosion proof equipment for catalyst drying andcalcining is required. The need for such equipment and procedures addsgreatly to the cost of the catalyst.

In contrast, the preferred method employed in the present invention forproducing ruthenium-promoted and other promoted cobalt catalystsutilizes a totally aqueous co-impregnation technique, followed by dryingand calcination of the resulting catalyst precursor. For noble metals,the promoter-metal is preferably either a promoter-nitrate, (e.g.,ruthenium (III) nitrosyl nitrate) or a promoter-chloride (e.g.,ruthenium (III) chloride).

We have discovered that, when aqueous co-impregnation solutions are usedcomprising the amounts of cobalt nitrate and ruthenium nitrate (orchloride) desired for the present invention, the ruthenium salt(s) will,unexpectedly, dissolve in the small amount of solution employed.Moreover, the ruthenium salts dissolve without the addition of acids orother agents and without heating. Although the reason for this result isunknown, it is believed that the acidity imparted to the solution by thecobalt nitrate may be at least partially responsible.

Acidic Aqueous Impregnation and/or Pretreatment of Support

As shown hereinbelow, the attrition resistances of γ-alumina supportsand of the catalysts produced therefrom are also unexpectedly improvedby (a) utilizing an acidic aqueous impregnation solution and/or (b)pretreating the catalyst support (preferably after calcination andbefore addition of the catalytic components) with an acidic aqueoussolution. In each case, the aqueous solution must have an acidity leveleffective for increasing attrition resistance. The aqueous cobaltimpregnation and coimpregnation solutions employed in the presentinvention typically have pH values within this range. However, nitricacid can be used, for example, to adjust the pH of the impregnationsolution, if necessary, or to form an appropriate pretreatment solution.

Catalyst Activation

To provide optimum performance, it is presently preferred that thecatalyst be activated/reduced in a hydrogen-containing gas by slowlyincreasing the temperature of the catalyst, preferably at a rate ofabout 0.5–2.0° C./minute, to approximately 250–400° C. (preferably about350° C.) and holding at the desired temperature for at least 2 hours.After reduction, the catalyst is preferably cooled in flowing nitrogen.

The reducing gas preferably comprises from about 1% to 100% by volumehydrogen, with the remainder (if any) being an inert gas, typicallynitrogen. The reducing gas is preferably delivered at a rate of about2–4 (preferably about 3) liters per hour per gram of catalyst. Thereduction procedure is preferably conducted in a fluidized bed reactor.The reduction procedure is most preferably conducted at conditions(i.e., temperature, flow rate, hydrogen concentration, etc.) effectiveto ensure that a very low water vapor partial pressure is maintainedduring the procedure.

The Fischer-Tropsch Reaction Process

The catalysts prepared and activated in accordance with the presentinvention can be employed in generally any Fischer-Tropsch synthesisprocess. For slurry bubble column and other three-phase reactionsystems, the catalyst will preferably be slurried in a Fischer-Tropschwax or in a synthetic fluid (e.g., a C₃₀ to C₅₀ range isoparaffinpolyalphaolefin such as that available from Chevron under the nameSYNFLUID) having properties similar to those of Fischer-Tropsch wax. Thecatalyst slurry will preferably have a catalyst concentration in therange of from about 5% to about 40% by weight based on the total weightof the slurry.

The synthesis gas feed used in the reaction process will preferably havea CO:H₂ volume ratio of from about 0.5 to about 3.0 and will preferablyhave an inert gas (i.e., nitrogen, argon, or other inert gas)concentration in the range of from 0 to about 60% by volume based on thetotal volume of the feed. The inert gas is preferably nitrogen.

Prior to initiating the reaction process, the activated catalyst willmost preferably be maintained in an inert atmosphere. Before adding thecatalyst thereto, the slurry fluid will preferably be purged withnitrogen or other inert gas to remove any dissolved oxygen. The slurrycomposition will also preferably be transferred to the reaction systemunder an inert atmosphere.

A particularly preferred SBCR reaction procedure comprises the steps of:(a) filling the SBCR, under an inert atmosphere, with the activatedcatalyst slurry; (b) heating and pressurizing the SBCR, under an inertatmosphere, to the desired pretreatment conditions (preferably atemperature in the range of from about 220° C. to about 250° C. and apressure in the range of from about 50 to about 500 psig); (c) replacingthe inert gas with hydrogen and holding the system at these conditionsfor from about 2 to about 20 hours; (d) purging the system with inertgas and lowering the reaction system temperature, if necessary, to apoint at least about 10° C. below the desired reaction temperature; (e)carefully replacing the inert gas with the desired synthesis gas; and(f) heating and pressurizing the reaction system, as necessary, to adesired operating temperature, preferably in the range of from about190° C. to about 300° C., and a desired operating pressure, preferablyin the range of from about 50 to about 900 psig.

EXAMPLES

In the following Examples, actual laboratory SBCR runs and two otherindependent testing techniques, the Jet Cup test and the ultrasonictest, were used, as indicated, to determine and characterize theattrition resistance properties of various catalysts. The Jet Cup andultrasonic techniques were found to simulate the attrition mechanismswhich occur in slurry bubble column reactors (i.e., fragmentation,abrasion, etc.).

A Jet Cup system 2 is illustrated in FIG. 3. The system comprises: asample cup 4; an air inlet tube 6, connected to the bottom of the samplecup; a settling chamber 8; and a fines collection assembly 10 includinga collection thimble 12. Before each test, the fines collection assemblywas weighed and its mass recorded. Five grams of sample were placed inthe sample cup and the sample cup was then attached to the settlingchamber. After all joints were sealed, humidified air (relative humidityof 60±5%) was passed at a controlled flow rate through the system forone hour.

The humidified air was introduced tangentially into the sample cup atthe bottom of the assembly and flowed out of the system through thethimble. The thimble was a cellulose filter which operated to retainfines carried out of the settling chamber by the air stream. In ordernot to interrupt the air flow during the test, two collection thimbleswere alternately used, with one thimble being quickly replaced by theother and weighed at 5 minutes, 15 minutes, and then 30 minutes into thetest. At the end of one hour, the air flow was stopped and the fines inthe thimbles, and also the coarse particles collected in the Jet Cup,were recovered and analyzed.

An ultrasonic test system 20 is illustrated in FIG. 4. The systemcomprises: a container 22; a 20 kHz Tekmar TM501 Sonic Disrupter 24equipped with a CV26 horn 26 and a 0.5 inch tip 28; and a horn supportframe 30. In each test, a pre-weighed sample was dispersed in 400 ml ofdistilled water by stirring. Each suspension had a solids concentrationof about 2.5 vol %. The suspensions were treated for 15 minutes at aSonic Disrupter setting of 350 watts. Because temperature is reported tobe a factor affecting ultrasonic energy output, a water bath was used tokeep the suspension temperatures relatively constant. At the end of eachrun, the slurry was transferred and sampled and then characterized usinga particle size analyzer. The remainder of the slurry was filtered andthen dried in an oven at 110° C. for sieving or for particle sizeanalysis.

The system used for characterizing the particulate samples generated inthe SBCR, Jet Cup, and ultrasonic tests, as well as the startingmaterials used, was a Leeds & Northrup Microtrac laser particle sizeanalyzer model 7990-11. Each SBCR and Jet Cup test sample was preparedfor analysis by pre-mixing the sample, placing the pre-mixed sample in50 ml of deionized water, and then dispersing the particulate samplematerial using an ultrasonic bath. Each of the resulting samplesuspensions had a particulate concentration of approximately 2.5 vol %.

After each ultrasonic test, the test suspension was stirred and portionswere drawn from the top, center and bottom of the suspension. Theseindividual portions were then analyzed in the particle size analyzer andthe portion results were averaged.

Example 1

Attrition resistance is defined in this Example as the percent reductionin particle size based on mean volumetric diameter, as measured using aMicrotrac particle size analyzer, after an approximately 240 hour run ina slurry bubble column reactor (SBCR). The attrition resistances of anumber of catalysts were compared. A series of 7 catalysts, varyingsignificantly with respect to the supports, preparation methods, andadditives used, were selected for this purpose. The catalystformulations tested were as follows:

CATALYST 1: (Non-promoted, γ-alumina-supported catalyst with 13 wt %Cobalt.)

Preparation Procedure:

CATAPAL B alumina from Condea/Vista in the boehmite form was calcined at500° C. for 10 hours to convert it to γ-alumina. It was then presievedto 400–0 mesh (i.e., a particle size of greater than 38 microns). Theγ-alumina was then impregnated with an aqueous solution of Co nitrate[Co(NO₃)₂.6H₂O], using an appropriate quantity to achieve incipientwetness (ca. 1.2 ml/g) with the desired loading of Co. The resultingcatalyst precursor was then dried in air at 115° C. for 12 hours andcalcined in air at 300° C. for 2 hours (with a heating rate of ca. 1°C./min to 300° C.).

Reduction Procedure Before Reaction:

The catalyst was reduced in 3000 cc/g/hr of pure hydrogen flow byheating at 1° C./min to 350° C. and holding for 10 hours.

CATALYST 2: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt,0.43 wt % ruthenium and 1 wt % lanthana.)

Preparation Procedure:

CATAPAL B alumina in the boehmite form was calcined at 600° C. for 10hours to convert it to γ-alumina. It was then presieved to 400–0 meshand impregnated in two steps. In the first step, the γ-alumina wasimpregnated with an aqueous solution of cobalt nitrate [Co(NO₃)₂.6H₂O],using an appropriate quantity to achieve incipient wetness (ca. 1.2ml/g) with the desired loading of cobalt. The resulting catalystprecursor was dried in air at 120° C. for 16 hours and calcined in airat 300° C. for 2 hours (with a heating rate of ca. 1° C./min to 300°C.). In the second step, the catalyst precursor was impregnated with anaqueous solution of lanthanum nitrate hexahydrate and ruthenium nitrosylnitrate using an appropriate quantity to achieve incipient wetness withthe desired loading of Ru and La₂O₃. The resulting catalyst precursorwas dried in air at 120° C. for 12 hours and then prereduced in purehydrogen at a flow rate of 720 cc/g/hr by the sequential steps of (a)heating the impregnated catalyst to 100° C. at a rate of 1° C./min andthen maintaining the catalyst at 100° C. for 1 hr, (b) heating thecatalyst to 200° C. at a rate of 1° C./min and holding at 200° C. for 2hours, and then (c) heating at a rate of 10° C./min to 360° C. andholding for 16 hours. Finally, the catalyst was cooled below 200° C.,purged with nitrogen, and cooled further. Air was bled into the nitrogenstream for 16 hours at a rate of ca. 1 cc air per 50 cc nitrogen perminute per 5 g of catalyst.

Reduction Procedure Before Reaction: Same as Catalyst 1.

CATALYST 3: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt,0.5 wt % ruthenium and 0.3 wt % potassium.)

Preparation Procedure:

Same as Catalyst 1 with the addition of ruthenium nitrosyl nitrate andpotassium nitrate in the cobalt nitrate solution used for impregnation.

Reduction Procedure Before Reaction: Same as Catalyst 1.

CATALYST 4: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt, 5wt % copper, and 4 wt % chromium.)

Preparation Procedure:

CATAPAL B alumina in the boehmite form was calcined at 500° C. for 10hours to convert it to γ-alumina. It was then presieved to 400–0 meshand impregnated with an aqueous solution of copper nitrate[Cu(NO₃)₂.xH₂O], and chromium nitrate [Cr(NO₃)₃.9H₂O], using anappropriate quantity to achieve incipient wetness (ca. 1.2 ml/g) withthe desired loading of Cu and Cr. The resulting precursor was then driedin air at 110° C. for 16 hours and calcined in air at 750° C. for 24hours (with a heating rate of ca. 1° C./min to 750° C.). Next, thecalcined precursor was impregnated with an aqueous solution of cobaltnitrate [Co(NO₃)₂.6H₂O] using an appropriate quantity to achieveincipient wetness with the desired loading of Co. The precursor was thendried in air at 115° C. for 12 hours and calcined in air at 300° C. for2 hours (with a heating rate of ca. 1° C./min to 300° C.).

Reduction Procedure Before Reaction: Same as Catalyst 1.

CATALYST 5: (Non-promoted, silica-supported catalyst with 20 wt %cobalt.)

Preparation Procedure:

The silica support (DAVISON Grade 952) was calcined at 500° C. for 10hours. It was then presieved to 400–250 mesh (i.e., a particle size of38–63 microns). A mixture comprised of the support and an aqueoussolution of cobalt nitrate [Co(NO₃)₂.6H₂O] was kneaded for 3.5 hours.The amount of the aqueous solution used was 110% of the pore volume ofthe silica support. The resulting catalyst precursor was next dried inair for 5 hours at 115° C. with moderate stirring and then calcined inair at 300° C. for 2 hours (with a heating rate of ca. 1° C./min to 300°C.).

Reduction Procedure Before Reaction:

The catalyst was reduced in 3000 cc/g/hr of pure hydrogen flow byheating at 1° C./min to 250° C. and holding for 10 hours.

CATALYST 6: (Zirconium-promoted, silica-supported catalyst with 20 wt %cobalt and 8.5 wt % zirconium.)

Preparation Procedure:

The silica support (DAVISON Grade 952) was calcined at 500° C. for 10hours. It was then presieved to 400–0 mesh and impregnated with anaqueous solution of zirconium oxonitrate [ZrO(NO₃)₂] using anappropriate quantity to achieve incipient wetness with the desiredloading of Zr. The Zr-loaded SiO₂ was then dried in an oven for 5 hoursat 115° C. with moderate stirring and calcined in air at 300° C. for 2hours (with a heating rate of ca. 1° C./min to 300° C.). The calcined,Zr-loaded silica was next impregnated with an aqueous solution of cobaltnitrate [Co(NO₃)₂.6H₂O] using an appropriate quantity to achieveincipient wetness with the desired loading of Co. The drying andcalcination processes were then repeated.

Reduction Procedure Before Reaction: Same as Catalyst 5.

CATALYST 7: (Zirconium-promoted, silica-supported catalyst with 20 wt %cobalt, 8.5 wt % zirconium, 0.5 wt % Ru and 0.3 wt % K.)

Preparation Procedure:

Same as Catalyst 6 with the addition of ruthenium nitrosyl nitrate andpotassium nitrate to the cobalt nitrate solution used in the secondimpregnation step.

Reduction Procedure Before Reaction: Same as Catalyst 5.

The catalytic properties for Fischer-Tropsch synthesis in a slurrybubble column reactor, as well as the attrition properties, of catalysts1–7 are shown in Table 1. These examples indicate that attritionresistance can vary significantly based upon the particular supports,preparation methods, and additives used. Based on 64 SBCR runs with awide variety of cobalt catalysts, including the above-describedcatalysts 1–7, having differing formulations and using either sphericalalumina or spherical silica supports, the average particle sizereductions for each category of support were as follows:

All Al₂O₃-supported Co catalysts 8.4% All SiO₂-supported Co catalysts13.7%

TABLE 1 SBCR Reaction and Attrition Results For Catalysts 1–7 ActivityAverage Particle Size Catalyst (g-HC/g- Selectivity Particle ReductionNo. Support Additives cat./h) % CH₄ α Size, (μm) (%) Catalyst 1 Al₂O₃ —1.07 10.9 0.85 85.6 8.4 Catalyst 2 Al₂O₃ La, Ru 1.31 — 0.81 67.7 4.3Catalyst 3 Al₂O₃ Ru, K 1.22 7.3 0.86 72.8 1.6 Catalyst 4 Al₂O₃ Cu, Cr0.23 10.9 0.78 79.5 4.3 Catalyst 5 SiO₂ — 0.67 7.6 0.83 107.1 12.2Catalyst 6 SiO₂ Zr 1.24 10.7 0.82 87.2 10.2 Catalyst 7 SiO₂ Ru, Zr, K0.90 9.9 0.88 82.4 14.2 The particle size is reported as the mean volumediameter as measured by a Microtrac particle size analyzer. The particlesize reduction was estimated from Microtrac measurements carried outbefore and after reaction (ca. 220–250 hours-on-stream) ReactionConditions: Catalyst weight: ca. 15 g, screened thru 150 × 400 mesh,calcined and reduced externally, T = 240° C., P = 450 psi, H₂/CO ratio =2, Total flow rate: ca. 15 L/min, Diluent: N₂: ca.60%

Example 2 Comparison of Attrition Results Obtained from Jet Cup,Ultrasound and SBCR Tests

A silica supported catalyst (Catalyst 5 in Example 1) which had shownrelatively low attrition resistance based upon the percent reduction inmean diameter after an approximately 240 hour SBCR run was used to gaugethe effectiveness and accuracy of the Jet Cup and ultrasonic testingtechniques. The Jet Cup and ultrasonic tests were conducted in themanner described above. FIG. 5 provides a comparison of the particlesize distributions of the silica supported cobalt catalyst before andafter (a) a SBCR run, (b) a Jet Cup test, and (c) an ultrasoundattrition test. As indicated in FIG. 5, the distributions obtained afterthe 20 minute ultrasound test and the one hour Jet Cup test comparedremarkably well with the particle size distribution obtained after a 240hour SBCR run.

Example 3 Comparison of Alumina, Silica, and Titania Supports

Various supports, with and without cobalt loading, were tested using theabove-described ultrasound and Jet Cup procedures. Prior to testing, thebare supports were calcined and presieved to 400–0 mesh in accordancewith substantially the same procedures used in preparing thecorresponding cobalt catalysts. The catalysts used for these tests wereas follows:

CATALYST 8: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt,0.43 wt % ruthenium, and 1 wt % lanthana.)

Preparation Procedure:

Same as Catalyst 2 except that the second impregnation step was carriedout with an acetone/ethanol (2:1) solution of lanthanum nitratehexahydrate and ruthenium acetylacetonate. The amount of solution usedwas ca. 2 ml/g.

The solvent was removed at 0.01 atm and 25–30° C. in a rotary evaporatorand the catalyst precursor was dried at 90° C. with moderate stirring.The precursor was then prereduced and passivated in accordance with thesame procedures employed for Catalyst 2.

Reduction Procedure Before Reaction: Same as Catalyst 2

CATALYST 9: (Zirconium-promoted, γ-alumina-supported catalyst with 20 wt% cobalt and 8.5 wt % zirconium.)

Preparation Procedure:

Same as Catalyst 1 with the addition of zirconium oxonitrate in thecobalt nitrate solution used for impregnation.

Reduction Procedure Before Reaction: Same as Catalyst 1.

CATALYST 10: (Non-promoted, silica supported catalyst with 20 wt %cobalt.)

Preparation Procedure:

Same as Catalyst 5 except for the use of incipient wetness impregnationrather than kneading with an excess volume of solution.

Reduction Procedure Before Reaction: Same as Catalyst 5.

CATALYST 11: (Zirconium-promoted, silica supported catalyst with 20 wt %cobalt and 8.5 wt % zirconium.)

Preparation Procedure:

Same as Catalyst 5 with the addition of zirconium oxonitrate in thecobalt nitrate solution used for impregnation.

Reduction Procedure Before Reaction: Same as Catalyst 5.

CATALYST 12: (Zirconium-promoted, silica-supported catalyst with 20 wt %cobalt and 8.5 wt % zirconium.)

Preparation Procedure:

Same as Catalyst 11 with the addition of zirconium oxonitrate in aseparate incipient wetness impregnation step after cobalt impregnationby the kneading method. The catalyst precursor was dried and calcinedafter the zirconium impregnation step by the same procedures as usedafter the cobalt impregnation step.

Reduction Procedure Before Reaction: Same as Catalyst 5.

CATALYST 13: (Non-promoted, titania-supported cobalt catalyst with 20 wt% cobalt.)

Preparation Procedure:

Anatase titania (DEGUSSA P25) was wetted to incipient wetness withdistilled water and then dried in an oven at 60° C. with moderatestirring. It was next calcined at 650° C. for 16 hours resulting in aca. 97% rutile support. The calcined titania was presieved to 400-0 meshand then impregnated with an acetone solution of cobalt nitrate[Co(NO₃)₂.6H₂O] using an appropriate quantity of solution to obtain aslurry with the desired loading of cobalt. Next, the resulting catalystprecursor was dried in a rotor evaporator at 25° C. and dried under avacuum at 140° C. for 16 hours. The precursor was then further calcinedin air at 250° C. for 3 hours. Finally, the dried catalyst wasrescreened to remove fines.

Reduction Procedure Before Reaction:

The catalyst was reduced in 1000 cc/g/hr of pure hydrogen by heating to350° C. and holding for 16 hours.

CATALYST 14: (Non-promoted, titania-supported cobalt catalyst with 20 wt% cobalt.)

Preparation Procedure

Anatase titania was wetted to incipient wetness with distilled water andthen dried in an oven at 60° C. with moderate stirring. It was nextcalcined at 350° C. for 16 hours to produce a support having primarilyan anatase structure. Next, the calcined titania was presieved to 400-0mesh and then impregnated in 2 steps. In the first step, the support wasimpregnated with an aqueous solution of cobalt nitrate [Co(NO₃)₂.6H₂O]using an appropriate quantity to achieve incipient wetness with 60% ofthe desired final loading of cobalt. This catalyst precursor was driedin an oven for 5 hours at 115° C. with moderate stirring. The driedprecursor was then calcined in air by raising its temperature at aheating rate of ca. 1° C./min to 250° C. and holding for 3 hours. In thesecond impregnation step, the remaining 40% of the cobalt was applied inthe same manner. The same drying and calcination procedures used in stepone were then repeated and the catalyst was rescreened to remove fines.

Reduction Procedure Before Reaction: Same as Catalyst 13

CATALYST 15: (Non-promoted, titania-supported cobalt catalyst with 12 wt% cobalt.)

Preparation Procedure:

Same as Catalyst 13, except that a cobalt loading of 12 wt % was formedrather than 20 wt %.

Reduction Procedure Before Reaction: Same as Catalyst 13.

The attrition test results for catalysts 8–15 are shown in Table 2. Theresults are presented in terms of the percentage of fines (particlesless than 16 microns) as measured by Microtrac analysis. The attritionresistance results show that, prior to cobalt impregnation, titania wasthe most attrition resistant support material, followed by alumina andwith silica trailing far behind. In contrast, however, a comparison ofthe results obtained for the cobalt catalysts produced using these samesupports shows that the γ-alumina-supported catalysts surprisingly hadthe highest attrition resistances.

TABLE 2 Attrition Resistances of Alumina, Silica, and Titania SupportsWith and Without Cobalt Loading (Ultrasound and Jet Cup Results) Fines(<16 μm) (%) Catalyst (Support/ Before Attrition After After Additives)Test Ultrasound Jet Cup CATAPAL B Alumina 0.9 7.0 10.8 Catalyst 8 0.73.6 1.9 (Al₂O₃/Co, La, Ru) Catalyst 9 0.8 6.1 5.9 (Al₂O₃/Co, Zr) DAVISONSilica 952 Grade 4.7 24.8 29.2 Catalyst 10 0 8.1 18.6 (SiO₂/Co) Catalyst11 0 5.5 8.6 (SiO₂/Co, Zr) Catalyst 12 0 8.5 15.6 (SiO₂/Co, Zr) Titania0 12 2.4 DEGUSSA P25 Catalyst 13 0.9 11.4 13.8 (TiO₂/Co) Catalyst 14 0.854.3 34.6 (TiO₂-Anatase/Co) Catalyst 15 (TiO₂-Rutile/Co) 4.1 10.8 19.6

Example 4 Effect of Preparation Method on the Attrition Resistance ofCobalt Catalysts having γ-Alumina Supports

The effects of various preparation methods, especially organic andaqueous methods of impregnation, on attrition resistance were determinedusing a series of SBCR runs. Each run lasted about 240 hours. The samealumina support, CATAPAL B manufactured by Condea/Vista, was used forall the catalysts. The catalysts also contained identical amounts ofruthenium and lanthana. The formulations of those catalysts tested butnot already described were as follows:

CATALYST 16: (γ-alumina-supported, cobalt catalyst with 20 wt % cobalt,0.5 wt % ruthenium, and 1 wt % lanthana.)

Preparation Procedure:

CATAPAL B alumina in the boehmite form was calcined at 750° C. for 16hours to convert it to γ-alumina. It was then presieved to 400-0 meshand impregnated in three steps (40%, 30%, and 30%)., each step utilizingan acetone solution of cobalt nitrate [Co(NO₃)₂.6H₂O], rutheniumacetylacetonate, and lanthanum nitrate [La(NO₃)₃.H₂O] in an appropriatequantity to achieve incipient wetness (ca. 1 ml/g) with the desiredloadings of cobalt, ruthenium, and lanthanum. Following each step, thecatalyst precursor was dried in a rotor evaporator at 40° C. for atleast 30 minutes and calcined in air at 300° C. for 2 hours.

The impregnated catalyst was then prereduced in 720 cc/g/hr of purehydrogen. The catalyst was first heated to 100° C. at the rate of 1°C./min and held for 1 hour. Next, the catalyst was heated to 200° C. ata rate of 1° C./min and held for 2 hours. The catalyst was then heatedat 10° C./min to a temperature of 360° C. and held for 16 hours.Finally, the catalyst was cooled to below 200° C., purged with nitrogen,and cooled further. Air was added to the nitrogen stream for 16 hours atca. 1 cc air per 50 cc nitrogen per minute per 5 g of catalyst.

Reduction Procedure Before Reaction: Same as Catalyst 8.

CATALYST 17: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt,0.43 wt % ruthenium, and 1 wt % lanthana.)

Preparation Procedure: Same as Catalyst 8.

Reduction Procedure Before Reaction: Same as Catalyst 8.

CATALYST 18: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt,0.43 wt % ruthenium, and 1 wt % lanthana.)

Preparation Procedure: Same as Catalyst 8, but using entirely aqueousimpregnation.

Reduction Procedure Before Reaction: Same as Catalyst 8.

CATALYST 19: (γ-alumina-supported cobalt catalyst with 20 wt % cobalt,0.43 wt % ruthenium, and 1 wt % lanthana.)

Preparation Procedure:

CATAPAL B alumina in the boehmite form was calcined at 750° C. for 16hours to convert it to γ-alumina. It was then presieved to 400–0 meshand impregnated with an aqueous solution of cobalt nitrate[Co(NO₃)₂.6H₂O] and ruthenium (III) nitrosyl nitrate [Ru(NO)(NO₃)₃.xH₂O]and lanthanum nitrate [La(NO₃)₃H₂O] using an appropriate quantity toachieve incipient wetness (ca. 1 ml/g) with the desired loadings ofcobalt, ruthenium and lanthanum. The catalyst precursor was then driedin air at 120° C. for 12 hours.

Pre-reduction Procedure:

The catalyst was then prereduced in 720 cc/g/hr of pure hydrogen. Thecatalyst was first heated to 100° C. at a rate of 1° C./min and held for2 hours. The catalyst was then heated at 10° C./min to a temperature of360° C. and held for 16 hours. Finally, the catalyst was cooled to below200° C., purged with nitrogen, and cooled further. Air was added to thenitrogen stream at ca. 1 cc air per 50 cc nitrogen per minute per 5 g ofcatalyst for 16 hours.

Reduction Procedure Before Reaction: Same as Catalyst 2.

The reaction and attrition results obtained with these catalysts andwith catalysts 2 and 8 are presented in Table 3. The catalysts listed inTable 3 had identical or substantially identical compositions, but wereprepared by different methods. Table 3 shows that the catalysts preparedby totally aqueous impregnation unexpectedly and surprisingly had higherattrition resistances than did the cobalt catalysts prepared by othermethods.

TABLE 3 Effect of Aqueous vs. Non-Aqueous Preparation Methods onCo/Al₂O₃ Attrition Resistance Activity Average Catalyst (g-HC/g-Selectivity Particle Particle Size No. Support Additives cat./h) % CH₄ αSize, (μm) Reduction (%)  8* Al₂O₃ La, Ru 1.42 12.5 0.80 73.6 8.1  8*Al₂O₃ La, Ru — — — 73.6 10.0  8* Al₂O₃ La, Ru 1.32 22.9 0.77 73.6 3.316* Al₂O₃ La, Ru 1.53 16.7 0.88 76.8 5.5 17* Al₂O₃ La, Ru 1.64 15.3 0.7970.1 14.4 17* Al₂O₃ La, Ru 1.80 15.2 0.89 81.4 10.4 18# Al₂O₃ La, Ru1.37 12.7 0.80 75.6 1.3  2# Al₂O₃ La, Ru — — — 64.6 0.3  2# Al₂O₃ La, Ru1.31  8.3 0.81 67.7 4.3 19# Al₂O₃ La, Ru 1.32 11.2 0.80 73.1 4.4*Catalysts preparation utilizing at least one organic impregnation step#Catalysts preparation utilizing totally aqueous impregnation Theparticle size is reported as the mean volume diameter as measured by aMicrotrac particle size analyzer. The particle size reduction wasestimated from Microtrac measurements carried out before and afterreaction (c.a. 220–250 hours-on-stream) Reaction Conditions: Catalystweight: ca. 15 g, screened thru 150 × 400 mesh, calcined and reducedexternally, T = 240° C., P = 450 psi, H₂/CO ratio = 2, Total flow rate:ca. 15 L/min, Diluent: N₂: ca.60%

Example 5 Effect of Lanthana Promotion on the Attrition Resistance ofCobalt Catalysts

We have also discovered that the attrition resistances of the cobaltcatalysts are unexpectedly and surprisingly enhanced by the addition ofa lanthana (La₂O₃) promoter. The improved attrition resistance providedby the addition of La₂O₃ is not detrimental to Fischer-Tropsch activity,or to Fischer-Tropsch selectivity. Preferred lanthana concentrationranges are provided hereinabove.

The following attrition resistance results were obtained from 47 slurrybubble column reactor runs using a wide variety of cobalt-on-aluminacatalysts, including the above-described alumina-supported catalystsdescribed in examples 1–4, having differing formulations. The resultsare expressed as the percent reduction in particle size of the catalystsbased on the difference in mean volumetric diameters of the catalysts asmeasured, using a Microtrac particle size analyzer, both before reactionin a slurry bubble column reactor and then after runs of approximately250 hours. The average particle size reductions for catalysts with andwithout lanthana were as follows:

Attrition Resistance (Ave. Particle Size Reduction) All Al₂O₃-supportedCo catalysts with La₂O₃ 6.6% All Al₂O₃-supported Co catalysts with La₂O₃prepared 5.2% using an aqueous impregnation method All Al₂O₃-supportedCo catalysts without La₂O₃ 9.2%

Example 6 Effect of Solution pH on the Attrition Resistance of AluminaSupports

In this example, CATAPAL B alumina samples calcined at 500° C. weretreated with aqueous solutions having pH values ranging from 1.0 to12.5. Acidic solutions were prepared using nitric acid in distilledwater. Basic solutions were prepared using ammonium hydroxide indistilled water. After being subjected to incipient wetness treatmentwith an acidic, neutral, or basic solution for 10 hours, each sample wasdried overnight at 120° C. and calcined again at 350° C. for two hoursto remove nitrate or ammonium ions. The treated samples were thenresieved to ensure that the particle size distribution of each samplewas from 45 to 90 microns.

The resulting aluminas were subjected to Jet Cup testing to determinetheir attrition resistances. The results of the tests, as measured byMicrotrac analysis, are presented in Table 5. The results surprisinglyrevealed that the most attrition resistant γ-aluminas were those treatedwith the low pH solutions, particularly those solutions having pH valuesof 5 or less (preferably 3 or less and most preferably from about 3 toabout 1).

As already mentioned, the preferred cobalt nitrate concentrationsemployed for aqueous impregnation and aqueous co-impregnation typicallyprovide particularly desirable pH values in the 1–3 range.

TABLE 4 Effect of pH on the Attrition Resistance of γ-Alumina (Jet CupResults) Mean Volume Diameter* 50% Passing Size* % Decrease % Decrease %Fines^(#) (<11 μm) Solution As Prepared after Jet As Prepared after JetAs After Jet pH Value (μm) Cup Test (μm) Cup Test Prepared Cup Test 1.071.9 27.3 69.5 25.3 0 4.5 3.0 72.7 29.4 70.3 26.7 0 6.6 5.0 73.5 31.771.1 27.7 0 6.7 7.0 72.8 32.8 70.3 29.9 0 8.1 10.0 71.0 35.6 68.5 31.8 010.5 12.5 72.5 35.3 69.8 31.5 0 10.1 Note: *Error = ±0.8; ^(#)= ±0.3

Example 7 Effect of Different Aluminas on the Catalytic Properties andAttrition Resistances of Cobalt-based, Fischer Tropsch Catalysts

The effect on attrition resistance and catalytic properties of the typeof alumina used was examined using a series of catalysts which, exceptfor the particular alumina supports employed, had the same formulations.Each of the alumina supports was manufactured by Condea/Vista. In eachcase, the alumina was calcined at 500° C. for 10 hours. All catalystswere prepared by incipient wetness impregnation and contained 20 wt %cobalt and 0.5 wt % ruthenium. The catalysts were prepared as follows:

CATALYST 20: (Ru-promoted, cobalt catalyst on CATAPAL B alumina with 20wt % cobalt and 0.5 wt % ruthenium.)

Preparation Procedure:

CATAPAL B alumina in the boehmite form was calcined at 500° C. for 10hours to convert it to γ-alumina. It was then presieved to 400-170 mesh(i.e., a particle size of greater than 38 microns and lower than 88microns) and impregnated with an aqueous solution of cobalt nitrate[Co(NO₃)₂.6H₂O] and ruthenium (III) nitrosyl nitrate [Ru(NO)(NO₃)₃.xH₂O]using an appropriate quantity to achieve incipient wetness (ca. 1.2ml/g) with the desired loading of Co and Ru. The catalyst precursor wasthen dried in air at 115° C. for 5 hours and calcined in air at 300° C.for 2 hours (with a heating rate of ca. 1° C./min to 300° C.).

Reduction Procedure Before Reaction:

The catalyst was reduced in 3000 cc/g/hr of pure hydrogen by heating at1° C./min to 350° C. and holding for 10 hours.

Each of the following catalysts 21–23 was prepared in the same manner ascatalyst 20. The specific supports employed in catalysts 21–23 were asfollows:

CATALYST 21: CATAPAL A support supplied by Condea/Vista and produced insubstantially the same manner as CATAPAL B.

CATALYST 22: CATAPAL D support supplied by Condea/Vista and produced insubstantially the same manner as CATAPAL B.

CATALYST 23: PURAL SB support supplied by Condea/Vista. The PURAL SB wasproduced by Condea/Vista in the same manner as CATAPAL B, but at adifferent plant.

The particular CATAPAL A, B, and D support materials employed incatalysts 20–22 were each determined to contain an amount of titania“impurity” of about 1000 ppm by weight (expressed as ppm by weight oftitanium) which was incidentally added, as part of the Ziegler Process,prior to the crystallization of the boehmite. In contrast, theparticular PURAL SB support material employed in catalyst 23 had beenformed by a blending process and was found to contain only about 500 ppmof titania. All of the supports employed in catalyst 20–23 werespherical, γ-alumina supports.

The CATAPAL A, CATAPAL B, and CATAPAL D materials were boehmites havingslightly different crystallite sizes. The crystallite sizes for thesematerials expressed in Ångstroms as determined by X-ray diffractionanalysis, were as follows:

CATAPAL A B D 020 plane 26 30 47 021 plane 41 43 72The crystallite sizes of the CATAPAL A and the CATAPAL B were relativelyclose. Thus, one would expect their physical properties to be similar.Moreover, the crystallite characteristics of the PURAL SB support weresubstantially identical to those of the CATAPAL B.CATALYST 24: (Ru-promoted, cobalt catalyst on γ-alumina with 20 wt %cobalt and 0.5 wt % ruthenium): The support, PURAL SB1, was supplied byCondea/Vista and was identical to PURAL SB except that the PURAL SB 1support was not doped with titanium.Preparation and Reduction Procedures: Same as catalyst 20.

The particular γ-alumina support, PURAL SB1, employed in catalyst 24 wasspecially produced for us by Condea/Vista. The PURAL SB1 was identicalto PURAL SB except that special efforts were made to prevent theaddition of titanium. An elemental analysis showed that the PURAL SB1support contained only 7 ppm of titanium.

Catalysts 20–24 were tested in a slurry bubble column reactor. Table 5Ashows the average activity and selectivity exhibited by each catalystover its first 24 hours of use. The same reaction conditions were usedin all of the SBCR runs (i.e., 230° C., 450 psig, and 900 l/hr of syngasand nitrogen with nitrogen comprising ca. 60% of the total feed gas).

TABLE 5A Activity and Selectivity of Co/Al₂O₃: Effect of DifferentAluminas CATALYST CATALYST CO SELECTIVITIES (Alumina WEIGHT CONV.ACTIVITY (% C) Support) (g) (%) (g/kg-cat/hr) CH₄ C₅+ Catalyst 20 15.321.8 1112.2 8.2 82.2 (CATAPAL B) Catalyst 21 27.4 44.6 1257.9 10.4 79.0(CATAPAL A) Catalyst 22 27.5 44.2 1261.9 10.9 79.0 (CATAPAL D) Catalyst23 21.5 36.3 1322.4 8.5 81.9 (PURAL SB) Catalyst 24 15.1 27.1 1340.0 8.480.5 (PURAL SB1)

The attrition resistances of the bare alumina supports used in catalysts20–24, prior to cobalt impregnation, were examined using the ultrasoundand the Jet Cup tests. The results obtained, as determined by Microtracanalysis, are shown in Tables 5B and 5C. Overall, the test resultsindicate that, although all of the supports were γ-aluminas, the aluminasupports having the higher titanium loadings exhibited noticeably betterattrition resistance. A comparison of the results obtained for theCATAPAL A, B, and D supports further shows that improved attritionresistance is obtained through the use of boehmites having crystallitecharacteristics closer to those of the CATAPAL A and CATAPAL Bmaterials.

TABLE 5B Attrition Resistances of Different γ-Aluminas (Results Beforeand After Ultrasound Attrition Test) Fines (<11 μm) (%) Alumina BeforeAfter CATAPAL A 0.3 0.5 CATAPAL B 0.0 4.3 CATAPAL D 0.4 7.8 PURAL SB 3.29.8

TABLE 5C Attrition Resistances of Different Aluminas (Results Before andAfter Jet Cup Attrition Test) Fines (<11 μm) (%)* Alumina Before AfterCATAPAL B 0 7.1 CATAPAL A 0 7.6 CATAPAL D 0.4 7.7 PURAL SB 2.8 17.6PURAL SB1 0 10.3 *Error = ±0.3

The attrition resistances of promoted cobalt catalysts 20–24 are shownin Tables 5D (ultrasonic results) and 5E (Jet Cup results). These testsreveal that, for all the aluminas used, the impregnation of cobaltsignificantly improved the attrition results obtained. Further, thecatalysts supported on the aluminas having higher titanium loadings hadsuperior attrition resistance.

TABLE 5D Effect of Different Aluminas on the Attrition Resistance ofCobalt Catalysts (Results Before and After Ultrasound Test) Fines (<11μm) Catalyst (%) (Alumina Support) Before After Catalyst 20 0 1.0(CATAPAL B) Catalyst 21 0.3 0.8 (CATAPAL A) Catalyst 22 1.5 1.8 (CATAPALD) Catalyst 23 2.2 4.8 (PURAL SB)

TABLE 5E Effect of Different Aluminas on the Attrition Resistance ofCobalt Catalysts (Results Before and After Jet Cup Test) Fines (<11 μm)Catalyst (%) (Alumina Support) Before After Catalyst 20 0 0.7 (CATAPALB) Catalyst 21 0 1.0 (CATAPAL A) Catalyst 22 0 2.9 (CATAPAL D) Catalyst23 0.4 10.5 (PURAL SB) Catalyst 24 0 5.2 (PURAL SB1)

These tests unexpectedly demonstrate that the presence of titanium inγ-alumina supports, particularly in an amount of more than 800 ppm byweight, or from about 800 ppm to about 2000 ppm, more preferably atleast about 1000 ppm and most preferably from about 1000 ppm to about2000 ppm, significantly improves the attrition resistance of the cobaltcatalysts produced therefrom. Except for differences in titaniumcontent, the CATAPAL B and PURAL supports employed in this Example wereall produced in the same manner. Additionally, the CATAPAL and PURALsupports were produced by the same manufacturer and were calcined in thesame manner. Moreover, the ruthenium-promoted cobalt catalysts formedtherefrom were identically produced, calcined, and reduced.

Example 8 Effect of Cobalt Loading on Catalyst Attrition Resistance

Since it was found that cobalt impregnation of γ-alumina significantlyimproves attrition resistance, the effect of cobalt loading wasinvestigated. A CATAPAL B alumina support which was determined to have atitanium loading of about 1000 ppm, and which was found to haverelatively high attrition resistance, especially when impregnated withcobalt, was selected for all the catalysts used in this example. Fourdifferent cobalt loadings were tested. The specific formulations ofthese catalysts were as follows:

CATALYST 25: (Ru-promoted, cobalt catalyst on CATAPAL B alumina with 15wt % cobalt and 0.4 wt % ruthenium.)

Preparation Procedure:

Same as Catalyst 20, but with only 15 wt % cobalt and 0.4 wt %ruthenium.

CATALYST 26: (Ru-promoted, cobalt catalyst on CATAPAL B alumina with 30wt % cobalt and 0.8 wt % ruthenium.)

Preparation Procedure:

Same as Catalyst 20, but with 30 wt % cobalt and 0.8 wt % ruthenium. Theimpregnation was accomplished in two steps using first a solutioncontaining 60% and then a second solution containing the remaining 40%of the required metal precursors. The second step was carried out afterdrying and calcining the partially loaded catalyst precursor. The dryingand calcining steps were then repeated after the second impregnation.

CATALYST 27: (Ru-promoted, cobalt catalyst on CATAPAL B alumina with 40wt % cobalt and 1.0 wt % ruthenium.)

Preparation Procedure:

Same as Catalyst 26, but with 40 wt % cobalt and 1.0 wt % ruthenium andusing three impregnation steps. The three impregnation steps applied40%, 30%, and then 30% of the metal precursors. Each step was followedby drying and calcining.

The attrition resistances of these catalysts, and of Catalyst 20, arecompared in Table 6. Table 6 also shows the activities of thesecatalysts as measured in a slurry bubble column reactor at 230° C. and450 psig. These results indicate that attrition resistance and activityincreased with increasing cobalt loadings up to 30 wt %.

TABLE 6 Effect of Cobalt Loading on Attrition Resistance (Jet Cup Test)Attrition Resistance Cobalt Loading Activity (g-HC/g- % Fines (<11 μm)Catalyst (wt %) cat/hr) After Jet Cup Catalyst 25 15 1.157 2.7 Catalyst20 20 1.240 0.8 Catalyst 26 30 1.666 0.3 Catalyst 27 40 1.505 0.4

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned above, as well as thoseinherent therein. While the invention has been described with a certaindegree of particularity, it is manifest that many changes may be madewithout departing from the spirit and scope of this disclosure. It isunderstood that the invention is not limited to the embodiments setforth herein for purposes of exemplification.

1. A γ-alumina catalyst support material having improved attritionresistance produced by a method comprising the steps of: (a) treating aparticulate γ-alumina material with an acidic aqueous solutioncomprising water and nitric acid and having a pH of not more than 5 andthen (b) after step (a) and prior to adding any catalytic material tosaid particulate γ-alumina material, calcining said particulateγ-alumina material at about 350° C.
 2. The γ-alumina catalyst supportmaterial of claim 1 wherein said acidic aqueous solution used in step(a) consists essentially of said water and said nitric acid and has a pHin the range of from about 3 to about
 1. 3. The γ-alumina catalystsupport material of claim 1 wherein said method further comprises thestep, after step (a) and prior to step (b), of drying said particulateγ-alumina material.
 4. The γ-alumina catalyst support material of claim3 wherein said particulate γ-alumina material is dried in said step ofdrying at a temperature of about 120° C.
 5. The γ-alumina catalystsupport material of claim 1 wherein said acidic aqueous solution used instep (a) consists essentially of said water and said nitric acid.